//create a IPageSource for the selected files then add each of the files to one source
foreach (string filename in OpFile.FileNames){// For each file add it to a source and collate them
SolidFramework.Model.Pdf.Pages.IPageSource source = model.CreateSource(filename); model.Insert(model.PageCount, source);}

For Each file selected add it to a new source and insert them into a single file: